----- Original Message -----
From: <RLVZ@aol.com>
> My first mistake was connecting the radial ground to my tower ground.
> Here's
> what fixed the Inverted L:
>
> 1) Disconnected the tower ground from the radial ground and the SWR
> improved.
> 2) Put in a new 10' ground rod at the base of the Inverted L and tied it
> into
> the radial ground and the SWR dropped further to 1.8 @ 1.77 Mhz @ Z=28.
I am presuming from your description that the tower is being used to support
the vertical run of a 160 1/4 wave inverted L.
If so, getting the SWR better by removing the connection to radials only
proves that the tower is in play with considerable induced current by virtue
of the large impedance change when the tower base termination is changed. If
the tower was not in play, removing the connection would have made little or
no difference.
One can construct a model of such a system where the tower actually carries
the majority of the current. Every conductor on the tower, in addition to
the tower itself, can be in play.
It's more likely that the tower ground which is likely fairly resistive at
RF is now dissipating a fair amount of power because the current ***which is
still being induced in the tower*** has to terminate in the lossy tower
ground, instead of the more efficient radial system.
The myth somehow still persists (consciously or unconsciously) that "the
antenna is radiating best when the SWR is best." SWR only shows that the
impedance match is close to 50 ohms resistive. Remember that a 50 dummy load
has a perfect SWR. Many excellent antennas lacking intrinsic 50 ohm match
points are a bear to feed power to, but worth it after the hard work is
done.
73, Guy.
K2AV
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|